Infinite play when opening another window.

If I start playing my score, and I open the Expression Maps Setup window during play, then playback continues past the end of the score, and keeps on going for God knows how long. Stops when I close the EMS window.

Is this a bug, or a feature?

I think you can consider it a feature that you can edit and change settings in dialogs during playback at all, and the fact that Dorico doesn’t stop playback until a modal dialog has closed a small glitch in that feature. It’s not one we’re likely to address in the near future.